Converting coal fired power stations to solar thermal chemical fuel

The Yallourn Power Station and the Hazelwood Power Station in Victoria are two of the most inefficient and CO2-intensive power stations in the world.

Hybrid solar-fossil systems for large-­scale solar energy storage

Michael Dolan & Daniel Roberts, University of Adelaide, February 7, 2013

Highly endothermic gasification and reforming processes offer a significant opportunity for the penetration of Concentrated Solar Power into the chemical and fossil energy industries. The upgraded products incorporate solar energy in chemical form which enables the ready storage, distribution and use of concentrated solar thermal energy.

Yallourn

The Yallourn Power Station produces about 22 percent of the electricity used in Victoria. Every hour 2,400 tonnes of brown coal are needed to produce super-heated steam for 4 turbines. These turbines have a combined capacity of  1,480 megawatts of electricity. In 2015 annual generated electricity output was 10,256 GWh, up from 9,806 GWh the year before.

In 2015 Yallourn Power Station installed a new High Pressure- Intermediate Pressure (HIP) turbine in Unit 2. This resulted in an efficiency improvement for Unit 2 of around 2.7%. This marked the completion of a 5 year program of new HIPs on all four Yallourn Units.

Hazelwood

The Hazelwood Power Station produces up to 25 percent of the electricity used in Victoria. Up to 15.3 million tonnes of brown coal are needed each year for an annual generated electricity output of approximately 12,000 GWh. Steam from 8 water tube boilers drives 4 turbine stages. These turbine stages have a combined capacity of  1,542 megawatts of electricity, just 62 megawatts more than the Yallourn Power Station.

Since 1996 more than $1 billion has been invested at Hazelwood to improve efficiency and reliability.

Lignite or brown coal from the Hazelwood mine is about 62 percent moisture at extraction.

Efficiency and CO2 Intensity

The brown coal used as fuel supplies about 9 gigajoules of thermal energy per tonne. The coal-fired power stations convert about 24 percent of this energy into electricity. The other 76 percent is output as waste heat.

Each tonne of brown coal contains about 250 kilograms of carbon and the balance, 750 kilograms, is mostly hydrogen and oxygen.

When burned the hydrogen and oxygen is converted to water vapour, while the 250 kilograms of carbon combines with oxyygen from the air to form 920 kilograms of carbon dioxide.

To generate 1 megawatt-hour of electricity at 24 percent efficiency, 1.667 tonnes of coal must be burned. This contains 417 kilograms of carbon that is converted to 1,528 kilograms of carbon dioxide when burned.

Solar Thermal Fuel in a Converted Coal Power Station

Brown coal can be converted into a mixture of gases using concentrated solar thermal energy.

One such process could convert each tonne of brown coal into 920 kilograms of carbon dioxide and 80 kilograms of hydrogen.

Solar thermal gasification of brown coal

The 80 kilograms of hydrogen gas from each tonne of coal supplies 9.67 gigajoules of thermal energy when burned.

This hydrogen fuel could be burned in one or more gas turbines added to an existing coal fired power station.

The hot exhaust gas from these gas turbines would be used to create superheated steam in the coal fired power station's existing boilers and drive some or all of its existing steam turbines.

The addition of the gas turbines fueled by hydrogen can raise the efficiency of the power station from just 24 percent to 60 percent.

The thermal energy available from the 80 kilograms of hydrogen fuel consists of the 9 gigajoules present in each tonne of pulverised coal together with 0.67 gigajoules of solar thermal energy.

At 60 percent efficiency this 9.67 gigajoules of thermal energy is converted into 5.8 gigajoules of electricity.

To generate 1 megawatt-hour of electricity at 60 percent efficiency, only 0.62 tonnes of coal must be converted to hydrogen that is burned.

This amount of brown coal contains 155 kilograms of carbon that is converted to 570 kilograms of carbon dioxide when it is gasified using concentrated solar thermal energy.

The hydrogen, 50 kilograms, from the 0.62 tonnes of brown coal is all that is required to generate 1 megawatt-hour of electricity.

There is a saving in mining operations because much less coal needs to be processed for each megawatt-hour of electricity generated: a reduction from 1.667 tonnes to just 0.62 tonnes of coal.

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Available technology boosts efficiency of thermal power plants to 60 per cent

.@MineralsCouncil Better: add GE gas turbine https://t.co/Ab0LVSbXPW, use steam in 2nd cycle, gasify coal. https://t.co/iyTYN2v4Mq #innovate

— Askgerbil Now (@Askgerbil) June 16, 2016